Digital BW, The Print

While it has been a while since I was in a lab with optical equipment and then it was having to do with Lasers and fiber optic transmission. But the number universally used for a measurable difference was 3 dB this value shows up in Audio and in RF measuring replace with f stop for photography the difference betwen f 2 and f 4 is 3 dB. It is roughly the anount of energy striking an area and an increase in energy of 4 is the normal value described as 3 dB.

If this translates to the print then for the average viewer looking from a normal distance which is usually considered to be when the viewed object covers 90 degrees of the viewing angle. Beyond 90 and you are into perherpheral vision where objects are noted but are not in focus.

So if you want to double the resolution of a 16 megapixel sensor you would need to replace it with a 64 megapixel sensor this is a function of squares so an increase from 16 to 32 yields a resolution increase of 1.4.

I also heard this stated in a class on photography at the National Archives receintly.

Just the ramblings of an old engineer.

Bill Lewis

Bill,

In going from f/4 to f/2.8 (one stop) the area, hence, the energy or power
received at the detector is increased by a factor of 2. Wouldn't the
increase then be 10log2 = 3db?  While, in your example, going from f/4 to
f/2 (two stops) increases the area by a factor of 4, so that the received
power also increases by a factor of 4, hence 10log4 = 6db.

Or did I misinterpret your statement?

Harry
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Harry F. Lockwood